Alkaline batteries have become increasingly more popular because of their high energy density. As such, these batteries are increasingly used in applications normally reserved for the traditional lead-acid battery systems.
In order to achieve extended battery life and efficiency in alkaline systems, the use of battery separators is required and the use of battery interseparators, as well, is preferred. The battery separators, when used for example in a nickel-cadmium battery, are located between the positive and negative plates so as to provide, (1) a separation between the electrodes of opposite charge, (2) an electrolyte reservoir, (3) a uniform electrolyte distribution across the electrode surface so as to permit uniform current density and (4) a space for electrode expansion.
Interseparators are located between the separators and the plates and provide the same properties as the separators except that interseparators do not normally prevent dendrisatic growth. Separators and interseparators in such systems must be porous, thin, chemically inert to alkaline electrolytes and posses a high degree of wicking properties.
By minimizing the thickness of the separator and/or interseparator one can minimize the amount of electrolyte required and maximize the energy density of the battery. Further, by having a high degree of wicking properties, for example, 5 cm/24 hours as determined by industry standards, one can maintain the electrolyte over the entire surface of the electrode, thereby further increasing the efficiency of the battery.
Battery separators and interseparators used in alkaline batteries at present are commonly formed of polypropylene, polyamide and/or nylon non-woven sheets.
Examples of separators and interseparators in use in alkaline systems today are shown in U.S. Pat. Nos. 4,264,691 and 4,330,602. The separator/interseparator is formed of synthetic pulp, alkali resistant inorganic filler and a long fiber of polyester, polyacrylic, polyamide or polyolefin materials. The separator/interseparator can be formed by a standard paper-making technique. The resultant material meets the desired requirements of thickness and wicking properties. The material however, often does not meet the required standards of tensile strength and filler retention necessary for the rapid development and use of alkaline batteries, especially for the automation of the manufacture of the batteries, particularly secondary alkaline systems, such as nickel-cadmium batteries.
The present invention overcomes the problems inherent in the currently used separators and provides an inexpensive sheet material with the desired tensile strength, chemical inertness, thickness and wicking properties and which is usable in automated assembly processes for forming alkaline batteries.